"Internal Server Error" and "Please enter package directory"

Hi folks,
just bought EasyBlog prof. and downloaded the file com_easyblog_3.9.15188_paid_j2.5.zip
I use Joomla 2.5.16

Tried to install it:
1. Upload package file:
shows after 1 minute: internal server error - look at error log file
What I see the uploaded file has 6,2 MB, allowed are 16 MB

As I can't find error log file after searching around with eXtplorer (even found nothing in /logs)
I downloaded the easyblog.pdf and tried Chapter 1: installing EasyBlog, page 4 "Install EasyBlog From Directory."

2. created the folder EasyBlog in /tmp and uploaded the zip-file "com_easyblog_3.9.15188_paid_j2.5.zip"
entered:
/tmp/EasyBlog

but no success: error "Please enter package directory"
I'm not sure: is /tmp directly under root?

Or whats the issue?
--